The invention is useful in water based hydraulic fluids and in water based metal working fluids.
Examples of hydraulic fluids are those fluids used in hydraulic machinery such as brake mechanisms, shock absorbers, control mechanisms and the like. The main classes of hydraulic fluids commonly used are petroleum-based, water/glycol solutions, water-in-oil emulsions, and oil-in-water emulsions.
There are several notable disadvantages to conventional hydraulic fluids. The petroleum-based hydraulic fluids pose certain environmental and health risks. In addition, petroleum oils may be flammable. Further, petroleum is a non-renewable and limited natural resource and, if allowed to escape into the ground, can cause soil and groundwater contamination and associated health and environmental problems.
Water based hydraulic fluids are used in machinery that is not exposed to freezing, or near-freezing, temperatures, such as machinery that is used in underground mining operations or near blast furnaces. Such fluids can contain numerous components so emulsifiers are used to obtain both the required formulation and stability. Existing water based hydraulic fluids, however, often lack the stability or lubricity required to operate at high temperatures and pressures.
Thus, there is a need for water based hydraulic fluids which have the characteristics of desirable shear stability, rheology control, lubricity, stability, volatility, very little swelling effect on (synthetic) rubber and anti-wear properties while reducing potential harm to the environment. Such a variety of desirable characteristics, which sometimes conflict, is difficult to achieve in a single composition.
In America whereas some metal working is still carried out with the aid of oil-based metal working fluids, the preponderance is done with water extendable fluids. Such fluids can contain numerous components (e.g., base oil, water, emulsifier, corrosion inhibitor, biocide) and emulsifiers are used to obtain both the required formulation and emulsion stability. There are three major types of water extendable metal working fluids: (1) “soluble oil” systems, which comprise a base oil, such as mineral oil, synthetic oil (polyolefins), synthetic esters and vegetable oil derivatives, with an emulsifying agent which disperses readily in water to form milky oil-in-water emulsions (e.g., about 85 weight percent of the base oil and about 15 weight percent emulsifier); (2) “synthetic” systems, which are aqueous dispersions comprising water and additives such as lubricating agents, corrosion inhibitors and the like and are substantially free of base oil; and (3) “semi-synthetic” systems, which are typically emulsions comprising aqueous solutions of emulsifying agents containing lesser amounts of highly dispersed base oil (e.g., about 5 to about 30 weight percent base oil). These metal working fluids are often supplied as concentrates which are then diluted with water, usually to form a 2 to 10% concentration, before being charged to the machines.
The selection of an effective metal working fluid for a specific application requires careful consideration of several properties. Whereas good lubrication and effective cooling are important, additional properties such as biostability, low foaming (maximizing contact with the tool and workpiece surfaces), emulsion clarity (allowing visualization of the workpiece), waste treatment and toxicity are often important factors in a given application.
Indeed, some of the most desirable properties are antithetical. In synthetic metal working fluids, for example, coarse-grained (larger) synthetic emulsions enhance lubricity but also form opaque emulsions, which decrease clarity. Reducing the emulsion particle size to improve the ability to see the workpiece is normally accompanied by reduced lubricity and undesirable foaming. It is believed that the foaming is caused by the formation of soaps resulting from the breakdown of the lubricant under high stress (poor lubricity) conditions. The foaming problem also can be exacerbated with the inclusion of certain commonly used corrosion inhibitors and other additives, for example antiwear additives.
Further, metal working fluids are susceptible to microbial attack by, for example, bacteria, fungi, and yeasts, causing one or more symptoms such as odor development, a decrease in pH, a decrease in dissolved oxygen concentration, changes in emulsion stability, increased incidence of dermatitis, workpiece surface-blemishes, clogged filters and lines, increased workpiece rejection rates, decreased tool life and generally unpredictable changes in coolant chemistry. Because biofouling is a major expense to some mills and metal working shops, biocides are sometimes added to metal working fluids to enhance stability and extend bath-life. However, biocides have a limited lifetime and present issues of regarding worker safety, so it is desirable to use a metal working fluid composition that is biostable without the need for biocides. Unfortunately, all metal working fluids must be discarded eventually, and the preferred method of waste treatment is through biodegradation. Traditionally, biostable compositions often complicate disposal and suffer a disadvantage from this perspective.
Esterified trimer acids (“ETAs”) are known to be useful in specific metal treatment fluid systems. They provide certain desirable properties, such as biostability, and can be disposed of using standard techniques. ETAs are derivatives of trimer acids, which, depending on the specific derivative, can be water immiscible or water dispersible. Water dispersible ETAs, for example, are useful in synthetic systems, whereas water immiscible ETAs (oil soluble) are ineffective in synthetic systems but useful in soluble oil systems.
Water immiscible ETAs are fully or nearly fully esterified with alkyl alcohols whereas water dispersible ETAs are partially esterified with alkylalkoxy alcohols only or in combination with alkyl alcohols but retain sufficient residual carboxylic acid groups which, when neutralized, render the derivatives water dispersible.
The different types of ETAs are used individually in different formulations depending on the type of emulsion desired. For example, U.S. Pat. No. 6,060,438 discloses the use of water immiscible ETAs, such as Priolube® 3953 (available from Uniqema, Del.) for use in semi-synthetic oil-in-water emulsions. The description of these water immiscible esters from the '438 patent is incorporated herein by reference. While such semi-synthetic systems are reported as having improved lubricity, biostability and reduced tendency to form soaps, they are opaque and cannot be used in applications where it is necessary or desirable to see the workpiece through the metal treatment fluid.
By contrast, U.S. Pat. Nos. 5,707,945 and 5,688,750 disclose the use of water dispersible ETAs, such as Priolube® 3951, Priolube® 3952 and Priolube® 3955 (available from Uniqema, Del.). The descriptions of water dispersible esters found in the '945 and '750 patents are incorporated herein by reference. Water extendable metal treatment fluids based on Priolube® 3951 emulsions are transparent and exhibit good boundary lubricity but experience high degrees of foaming. Water extendable metal treatment fluids based on Priolube® 3952 exhibit good boundary lubricity but are milky. Water extendable metal treatment fluids based on Priolube® 3955 exhibit good lubricity and are moderate foaming and translucent, turning to opaque.
Unfortunately, even with the advancements provided by the ETA technology, it has not been possible to provide a synthetic (water based) emulsion system that exhibits good lubricity, transparency, low foaming, and is both biostable and waste treatable. Thus, the selection of an appropriate water extendable metal working fluid for a given application required a decision as to which desirable property should be sacrificed at the expense of others. For this reason, synthetic metal working fluids are typically used in applications where cooling is the primary criterion, whereas the semi-synthetic and oil soluble fluids are used in applications where lubricity is more important.
Accordingly, there remains a need in the art for synthetic (water based) emulsion systems that exhibit good lubricity, transparency, low foaming, and that are both biostable and waste treatable.